Apparatus for monitoring thread tension

ABSTRACT

Apparatus for monitoring thread tension in a plurality of threads employed in a power driven machine having at least one needle and a plurality of threads which comprises a plurality of means for sensing the tension of individual threads and operatively connected means for individually adjusting the tension of each sensor means. A preferred apparatus is an electromechanical thread tension device which further includes an electrical switch associated with the means for sensing thread tension. A particularly preferred apparatus which is suitable for monitoring chain stitches produced by sewing and like machines comprises the electromechanical thread tension device, gating assembly means for detecting thread tension during the period when the stitch is being set, and an electrical control system designed to produce a warning signal and/or mark the fabric and/or stop the machine in the event of insufficient thread tension.

United States Patent [191 Brandriff et al.

Wilcox, P.O. Box 503, Dover, NJ. 07801 [22] Filed: Dec. 9, 1971 [2!] App]. No.: 206,432

[52] U.S. Cl. 112/218 R, 200/6l.18 [51] Int. Cl B65h 59/10 [58] Field of Search 112/218 R, 219 R,

[56] References Cited UNITED STATES PATENTS 4/I954 Schwartz 112/219 R 3/1964 Bryson 1l2/219 R Primary Examiner-H. Hampton Hunter Attorney-Richard N. Miller Jan. 15, 1974 [5 7] ABSTRACT Apparatus for monitoring thread tension in a plurality of threads employed in a power driven machine having at least one needle and a plurality of threads which comprises a plurality of means for sensing the tension of individual threads and operatively connected means for individually adjusting the tension of each sensor means. A preferred apparatus is an electromechanical thread tension device which further includes an electrical switch associated with the means'for sensing thread tension. A particularly preferred apparatus which is suitable for monitoring chain stitches produced by sewing and like machines comprises the electromechanical thread tension device, gating assembly means for detecting thread tension during the period when the stitch is being set, and an electrical control system designed to produce a warning signal and/or mark the fabric and/or stop the machine in the event of insufficient thread tension.

10 Claims, 8 Drawing Figures APPARATUS FOR MONITORING THREAD TENSION BACKGROUND OF THE INVENTION This invention relates to an apparatus for monitoring thread tension in a plurality of threads or strands utilized by a power driven machine having at least one needle and a plurality of threads which comprises means for sensing the tension of individual threads and means for individually adjusting the tension of each sensor means. More particularly, the invention relates to an electromechanical thread tension apparatus and to a chain stitch monitoring apparatus comprising the electromechanical thread tension device, gating assembly means for detecting thread tension when the stitch is being set, and an electrical control system.

Many thread tension monitoring devices have been utilized in the past which detect thread breakage or thread failure of upper and/or lower thread in sewing and embroidering machines and operate a control device such as a stop motion mechanism, warning light or audio signal, thereby minimizing the number of idle or unbound stitches. For example, spring-loaded and gravity devices have been utilized to detect thread breaks and thread failures in thread sections under continuous tension. Other electromechanical devices have been mounted on the sewing machine head to detect breaks or run-outs in either upper or lower threads. Some of the electromechanical devices have employed the slack developed in either the upper or lower thread of sewing machines to operate an electrical contact located adjacent to the needle to actuate the control mechanism in the event of thread break or failure. Finally, still other devices have employed periodic thread tension sensors in combination with oscillatable circuit interrupting or electrical time delay means to detect thread breaks or failure.

Heretofore, it has not been possible to detect skipped stitches as the foregoing devices were directed primarily to detecting thread breaks and thread failure or runout. Further, the prior art devices did not include individually adjustable tension sensing elements and exhibited a number of other shortcomings. For example, the continuous tension-type devices were subject to wide variations in thread tension and were unable to detect skipped stitches arising from problems in the needle area. Also, these devices were often difficult to operate because of the need to pass the thread through small eyes or loops in the tension sensors. Some such devices were applicable only to upper threads and, therefore, lower threads were not monitored. n the other hand, the periodic tension devices in combination with circuit interrupting means included an electromechanical device mounted on the head of the machine where it was subject to malfunction due to vibration, lint, and dust. These same problems applied to electromechanical devices which were mounted on the head of a sewing machine to control either the tension or sense the slack in the lower bobbin or looper thread. Finally, all devices mounted on the head required additional set-up time because of their complicated nature and space limitations.

The inability of the prior art devices in detection of skipped stitches has been particularly troublesome with the advent of high-speed, chain stitch sewing and embroidering machines. The chain stitch is employed in the high-speed machines because large spools of thread can be used to feed the looper, thereby assuring long sewing cycles. In contrast, lock stitching is characterized by short sewing cycles due to the limited thread capacity of the bobbin. However, chain stitches have the disadvantage that one incomplete stitch causes a failure in the entire chain of stitches.

Despite the foregoing disadvantage of chain stitches, such stitches are widely used in decorative stitching operations where multiple rows of evenly spaced stitches are required such as in the manufacture of vinyl door panels for automobiles. On the other hand, multiple rows of chain stitches are employed in the manufacture of vinyl-covered, foam rubber automobile seats, tents, and quilting materials. In addition, double rows of chain stitches are used in manufacturing flags,

air bags for autos, and in ammunition powder charge bags.

Thus, there is a need for stitch monitors on the highspeed, multi-needle, chain stitch sewing and embroidering machines because large quantities of material pass through the machine before the damage is detected by an inspector or the operator. Such devices minimize the quantities of scrap or rework material resulting from a skipped stitch and the consequent failure of the entire chain of stitches. In addition, these devices reduce the instances where additional work is done on the material before the defect is discovered thereby achieving cost savings. The devices also reduce the occasions where the defect goes unnoticed with the consequent loss of life such as in the manufacture of parachutes.

SUMMARY OF THE INVENTION Generally, this invention relates to an apparatus for monitoring the thread tension in a plurality of threads or strands employed in a power driven machine utilizing plural threads and at least one needle which comprises a plurality of means for sensing the tension of individual threads and operatively connected means for individually adjusting the tension of each sensor means. A preferred tension monitoring apparatus is an electromechanical device which comprises an electrical switch in combination with the foregoing apparatus.

A further aspect of the present invention is an apparatus for monitoring stitches produced by a chain stitch sewing machine using a plurality of threads and at least one needle which comprises the electromechanical thread tension detector apparatus in combination with gating assembly means for detecting tension only during the period when either thread tension is at least about one-half its maximum or the stitch is being set and an electrical circuit which includes a power supply, the electrical switch, the gating assembly means, and a control means actuable in response to insufficient thread tension.

The inventive apparatus is simple, compact, and can be readily attached to a conventional sewing machine, for example, in a location remote from the head. Also, the apparatus does not substantially increase the time required to set up a machine because it is simple and easy to thread. Further, the tension of each of the tension elements is adjustable thereby facilitating accurate control. Finally, control is achieved without complex electrical time delay or interrupter means.

BRIEF DESCRIPTION OF THE DRAWINGS Specific embodiments of the invention have been chosen for purposes of illustration and description and are shown in the accompanying drawings wherein:

FIG. 1 is a side elevation view showing a sewing machine for producing chain stitches with the thread tension monitoring apparatus of this invention attached on the upper and lower thread lines;

FIG. 2 is a front elevation view of the electromechanical thread tension detector of the invention;

FIG. 3 is a right side elevation view, partly fragmented (part of plastic removed), of the thread tension detector of FIG. 2;

FIG.4 is a transverse vertical section taken on line 4 4 of the thread tension detector of FIG. 2;

FIG. 5 is a plan view of a horizontal section taken on line 5 5 of the thread tension detector of FIG. 2;

FIG. 6 is a right side elevation view of the handwheel and gating assembly of the sewing machine of FIG. 1;

FIG. 7 is a transverse vertical section of the gating assembly taken on line 7 7 of FIG. 6 and FIG. 8 is an electrical circuit diagram of the control element of the stitch monitor apparatus.

DETAILED DESCRIPTION Referring now to FIG. 1 of the drawings, the described stitch monitoring apparatus is embodied in a conventional chain stitch sewing machine 10 having a bracket arm 12 terminating in head 14 in which there is mounted a reciprocating needle bar 16 carrying twin needles 18a and 18b at its lower end. The sewing machine is mounted on a base or table 26 which may be supported in any convenient manner. Twin loopers 27 are mounted below the surface of table 26 and cooperate with needles 18a and 18b in a known manner. Presser foot 20 is mounted behind needles 18a and 1812. Also, mounted in the head 14 is the vertically moving take up lever 22 provided with conventional thread eyes 23 and 24 (not shown) at its outer end.

The electromechanical thread tension detector '28 is attached by suitable fasteners (not numbered) to sensor mounting plate 32 which is mounted on the front of sewing machine 10 by suitable means such as threaded fasteners 34a.

FIGS. 2 5 show the details of electromechanical thread tension detector 28 which comprises a tension sensor assembly including tension sensing elements 420, b, c, and d (FIG. 2), sensing element adjusting block 38, and sensing element adjusting means 40; and lower and upper thread guides 44 and 45, contact bar 46, and means 48 and 50 for electrically connecting contact bar 46 and adjusting block 38 with the electrical circuit containing the control element. The electromechanical thread tension detector assembly is electrically insulated from the sewing machine 10 and part of the environment by base plate 52 and cover plate 54 which are made of an insulating material such as the clear polycarbonate sold by General Electric under the trade name Lexan." Sensing elements 42a, b, and d are made of electrically conductive wire and each element is mounted in an adjustable segment (FIG. 5) of adjusting block 38.

Details of the manner of adjustment of sensing element 42b are shown in FIG. 4. For this purpose, tension sensing wire 42b passes through a circular opening in threaded sensing wire adjusting stud 58b. The tension in sensing wire 42b may be set by mounting the assembly 28 in a jig with the sensing wire in a horizontal position, hanging a weight of predetermined mass therefrom, and tightening or loosening adjusting nut 60 until wire 42b contacts bar 46 as can be shown by a lamp and current source connected to electrical leads 48 and 50. In this manner, precise tension measurement and control is obtained. In a similar way, each of the sensing elements is adjusted.

FIG. 1 further shows lower threads 61 and 62 and upper threads 64 and 66 passing through thread tension units 68, over upper or lower thread guides 44 and 45, around a thread tension sensing wire, and back over the other of thread guides 44 or 45. Upper threads 64 and 66 then pass over thread guide means 70, through thread guide loops 72, and through eyes 23 and 24 (not shown) on vertically moving take-up lever 22 to needles 18a and 18b. Similarly, lower looper threads 61 and 62 then pass through conventional thread guide loops 74, 75, and 76 each having single or multiple eyes which can be of the type shown on thread guide loop 76 and pass through looper tension nipper 78 and conventional looper take-up means (not shown) to twin loopers 27.

The physical arrangement of the threads is such that at the time the thread tension is periodically checked when a stitch is being set or the thread tension is about at least one-half of the maximum each thread is under tension and such tension holds individual sensing elements 42a, b, c, and d, etc. away from contact bar 46. At the tension measuring point in the described embodiment, the minimum tension on the upper threads is about 26 grams and the minimum tension on the lower looper threads is about 10 grams. Because of the pulley effect of thread guides 44 and 45, the sensor elements oft he upper threads are adjusted for about 40 grams of thread tension which will hold the element away from contact bar 46. Similarly, the lower thread elements are adjusted for about 15 grams of tension in order to prevent contact from being made. During the remainder of the stitching cycle the balance of the handwheel revolution the upper thread will be slack as the take-up lever 22 moves down and tension will increase as it moves to its uppermost point where the tension on all threads is checked. The tension on the looper thread changes in a like manner.

FIG. 6 shows the location of the gating assembly means with respect to handwheel 80. Photoelectric assembly 84 mounted on bracket 94 is located on a radius of the handwheel 80 about 45 from the vertical.

FIG. 7 shows the details of a preferred gating assembly of the optical type which controls the period during which the tension in the individual threads is sensed and measured. In the arrangement depicted, handwheel 80 has a circular opening 82 bored therein at a point thereon which corresponds to the approximate peak tension coincident with the setting of the stitch. The electrical circuit depicted in FIG. 8 is activated or closed by a photoelectric assembly 84 which comprises light-emitting diode 86, phototransistor 88, electrical connectors 90, and aligned apertures 92 and 93. Photoelectric assembly 84 is mounted on bracket 94 with fastening means such as fasteners 96 and the other end of the bracket 94 is fastened to sewing machine 10, The phototransistor 88 closes the electrical circuit each time the opening 82 in the handwheel 80 is aligned with apertures 92 and 93 because electrical current passes through the transistor when light from the lightemitting diode impinges thereon.

FIG. 8 discloses the details of a preferred electrical circuit. Generally, the circuit includes a power supply system or source of current, a gating sensor assembly, a gating sensor amplifier system, a thread tension sensor electrical switch, and control means actuable in response to a thread tension insufficiency.

Referring to FIG. 8, transformer 100, bridge rectifier 102, resistors 104 and 106, capacitors 108 and ll0, zener diode 112, and transistor 114 comprise the power supply system which changes alternating current from power leads 98 and 99 to direct current of a constant reduced voltage which may range from about to 20 volts. The power supply provides current to the light-emitting diode 86 of the gating assembly through resistor 116 and provides current to phototransistor 88 through resistor 118.

During the period when light from light-emitting diode 86 is blocked by the handwheel, current flows though resistors 118 and 120 to activate transistor 122 which causes current to flow through resistor 124 to activate transistor 126, thereby causing current to flow through resistor 128 and transistor 126 to ground 130. Resistors 118, 120, 124, and 128 and transistors 122 and 126 comprise the gating signal amplifier system.

In operation, when phototransistor 88 is actuated by light from light-emitting diode 86, the current flowing through resistor 118 is directed to ground 130 through the phototransistor 88. In such case, current ceases to flow through resistor 120 thereby inactivating the remainder of the gating signal amplifier system. Thus, current flows through resistor 128 charging capacitor 132 until sufficient voltage is achieved to close silicon unilateral switch 134 and to complete the circuit to ground 130 through both resistor 136 and the capacitor 138 and resistor 140 in series. In addition, current is available to the thread sensor switch 142 which comprises contact bar 46, adjusting block 38 in combination with metal sensing element 42, and electrical connectors.

In the event of a skipped stitch, thread tension is insufficient to prevent thread tension sensor element 42 from contacting bar 46 thereby completing the circuit by closing thread sensor switch 142 and causing current to flow from capacitor 138 through sensor switch 142, diode 144, and resistor 146 into the gate of silicon controlled rectifier 148. Capacitor 150 and resistor 152 form a noise suppression network for the silicon controlled rectifier 148 which is desirable, but not essential. Application of current to the gate of silicon controlled rectifier 148 causes current to flow through resistor 154 thereby lighting indicator lamp 156. This light 156 remains on until reset switch 158 is manually actuated and released. Alternatively, a relay, marking device, counting system, or an alarm may be substituted for the indicator lamp. However, a preferred arrangement would include a relay, alarm or marking device in parallel with the indicator lamp to provide a dual indicating control means.

In the described stitch monitoring apparatus, an equivalent actuating means may be substituted for the photoelectric system employed in the gating assembly means. For example, the actuating means may consist of a cammed surface on the handwheel which makes contact with an electrical conductor element to close the circuit at a time in the cycle when the stitch is being set and the threads are under tension. Alternatively, a magnet mounted on the handwheel in combination with a reed switch may serve as the actuating means. Also, a commutator and brush arrangement may function as the actuating means. Another suitable means would consist of a protrusion on the handwheel passing through a light beam whereby the circuit is closed when the light beam is broken. Thus, while the photoelectric actuating means is preferred, obvious equivalents may be substituted therefor.

In like manner, a variety of electric circuits may be substituted for the electrical circuit disclosed in the illustrated embodiment. Of course, an equivalent circuit must include the essential elements in the described circuit, namely, a power supply, electrical means actuated by the gating assembly, an electrical switch associated with the thread tension sensor assembly, and control means actuable in response to an insufficient thread tension.

Finally, the electromechanical thread tension sensor assembly comprising the adjustable tension sensor assembly and the electrical switch associated therewith also may be modified. For example, non-metallic tension sensing elements having an electrical contact mounted thereon may be substituted for the metallic elements illustrated. In addition, a sensing element of triangular, rectangular, or other cross section may be substituted for the described elements of circular cross section. Obviously, the size, shape, and cross section of the individual segments in the adjusting block may be modified, too. Also, the design and location of the means for adjusting the tension of each sensor element may be changed, including employment of more than one adjusting means in combination with each sensor element for greater sensitivity. The contact bar may be relocated behind the sensor elements in order to control development of excessive thread tension such as in thread feeds to tufting machines.

While the stitch monitoring apparatus has been illustrated on a two needle, chain stitch, sewing machine, it is particularly suitable for use on multi-needle machines having, for example, four, six or l2 needles. Such an apparatus is operable whether these machines operate at low, intermediate or high speeds.

The electromechanical adjustable tension sensor assembly, on the other hand, may be utilized on almost any power driven machine employing at least one needle and thread. In addition to both chain stitch and lock stitch sewing machines, the adjustable tension sensor assembly may be employed on embroidering, tufting, quilting, knitting or weaving machines, etc., for detecting thread break and/or thread failure and/or stitch failure and/or excess tension. Further, this detector device operates in either the forward or reverse stitching direction of such machines.

While the invention has been described with reference to certain embodiments, it is not intended that such embodiments shall be regarded as limitations upon the scope of the invention. It will be obvious to those skilled in the art that other modifications and variations of the invention can be made and various equivalents of the invention can be made and various equivalents substituted therein without departing from the principles disclosed.

What is claimed is:

1. An apparatus for monitoring the tension in a plurality of threads or strands utilized by a power driven machine having at least one needle and a plurality of threads which comprises a plurality of means for sensing the tension of said threads, each of said means sensing the tension in an individual thread in contact therewith, and a plurality of means for individually adjusting the tension of each means for sensing, said means for adjusting comprising an adjusting stud and nut assembly operatively connected to said means for sensing.

2. An apparatus in accordance with claim 1 wherein said means for sensing tension comprises an electrically conductive metal sensor element.

3. An apparatus in accordance with claim 1 wherein each said means for adjusting tension includes a segmented block having an individual means for sensing tension mounted in an adjustable segment thereof, said adjusting stud being mounted in said segmented block whereby the base of said sensing means passes through an opening in said stud in the end opposite from the nut and the tension value of each means for sensing is set by adjusting said nut on said stud against the side of said block opposite each segment.

4. An apparatus in accordance with claim 3 which includes in addition an electrical switch associated with said means for sensing tension which is adapted to be opened or closed in the event of insufficient thread tension.

5. An apparatus in accordance with claim 4 which includes, in addition, an electrical circuit comprising a power supply, said switch, and control means actuable in response to a thread tension insufficiency.

6. An apparatus in accordance with claim 4 wherein said electrical switch comprises an electrically conductive metal sensor element, an electrically conductive contact bar, and means for electrically connecting said element and said bar with an electric circuit containing a control element for the power driven machine.

7. An apparatus for monitoring the tension in a plurality of threads or strands utilized by a power driven machine having at least one needle and a plurality of threads which comprises a plurality of means for sensing the tension of said threads, each of said means sensing the tension in an individual thread in contact therewith, a plurality of means for individually adjusting the tension of each means for sensing; and gating assembly means electrically connected to said means for sensing whereby said means for sensing tension detect thread tension during the period when the stitch is being set and when the tension of each thread is at least one half its maximum.

8. An apparatus in accordance with claim 7 wherein said means for sensing the tension of each thread comprises an electrically conductive metal tension sensor element for each thread; said means for adjusting tension includes a segmented block with each sensor element being mounted in an adjustable segment thereof, an adjusting stud and nut assembly for each sensor element being mounted in said segmented block whereby the base of said sensing means passes though an opening in said stud in the end opposite from the nut and the tension value of each means for sensing is set by adjusting said nut on said stud against the side of said block opposite each segment; and which includes, in addition, an electrical switch associated with said means for sensing tension which is adapted to be opened or closed in the event of insufficient thread tension and an electrical circuit comprising a power supply, said electrical switch, said gating assembly means, and a control means for the power driven machine actuable in response to insufficient thread tension.

9. An apparatus in accordance with claim 8 wherein said gating assembly means comprises a light source, an aperture in the sewing machine handwheel, and the means actuated by said light source is a phototransistor, said phototransistor being actuated when said aperture is in alignment with said light source and the phototransistor.

10. An apparatus in accordance with claim 9 wherein said electrical circuit includes, in addition, a gating sensor assembly amplifier system. 

1. An apparatus for monitoring the tension in a plurality of threads or strands utilized by a power driven machine having at least one needle and a plurality of threads which comprises a plurality of means for sensing the tension of said threads, each of said means sensing the tension in an individual thread in contact therewith, and a plurality of means for individually adjusting the tension of each means for sensing, said means for adjusting comprising an adjusting stud and nut assembly operatively connected to said means for sensing.
 2. An apparatus in accordance with claim 1 wherein said means for sensing tension comprises an electrically conductive metal sensor element.
 3. An apparatus in accordance with claim 1 wherein each said means for adjusting tension includes a segmented block having an individual means for sensing tension mounted in an adjustable segment thereof, said adjusting stud being mounted in said segmented block whereby the base of said sensing means passes through an opening in said stud in the end opposite from the nut and the tension value of each means for sensing is set by adjusting said nut on said stud against the side of said block opposite each segment.
 4. An apparatus in accordance with claim 3 which includes in addition an electrical switch associated with said means for sensing tension which is adapted to be opened or closed in the event of insufficient thread tension.
 5. An apparatus in accordance with claim 4 which includes, in addition, an electrical circuit comprising a power supply, said switch, and control means actuable in response to a thread tension insufficiency.
 6. An apparatus in accordance with claim 4 wherein said electrical switch comprises an electrically conductive metal sensor element, an electrically conductive contact bar, and means for electrically connecting said element and said bar with an electric circuit containing a control element for the power driven machine.
 7. An apparatus for monitoring the tension in a plurality of threads or strands utilized by a power driven machine having at least one needle and a plurality of threads which comprises a plurality of means for sensing the tension of said threads, Each of said means sensing the tension in an individual thread in contact therewith, a plurality of means for individually adjusting the tension of each means for sensing; and gating assembly means electrically connected to said means for sensing whereby said means for sensing tension detect thread tension during the period when the stitch is being set and when the tension of each thread is at least one half its maximum.
 8. An apparatus in accordance with claim 7 wherein said means for sensing the tension of each thread comprises an electrically conductive metal tension sensor element for each thread; said means for adjusting tension includes a segmented block with each sensor element being mounted in an adjustable segment thereof, an adjusting stud and nut assembly for each sensor element being mounted in said segmented block whereby the base of said sensing means passes though an opening in said stud in the end opposite from the nut and the tension value of each means for sensing is set by adjusting said nut on said stud against the side of said block opposite each segment; and which includes, in addition, an electrical switch associated with said means for sensing tension which is adapted to be opened or closed in the event of insufficient thread tension and an electrical circuit comprising a power supply, said electrical switch, said gating assembly means, and a control means for the power driven machine actuable in response to insufficient thread tension.
 9. An apparatus in accordance with claim 8 wherein said gating assembly means comprises a light source, an aperture in the sewing machine handwheel, and the means actuated by said light source is a phototransistor, said phototransistor being actuated when said aperture is in alignment with said light source and the phototransistor.
 10. An apparatus in accordance with claim 9 wherein said electrical circuit includes, in addition, a gating sensor assembly amplifier system. 